Originally derived from "You're a fucking shithead" it has gone through several stages of evolution to reach its classy status. Typically it is used in good fun both on the internet and in real time conversation. You may note how the smooth syllables roll of of the tongue. YAFS can also be used to cause emotional devastation as well. Its dedicated to all those deserving of this title.
1.) "You're a Fucking Slut"
2.) "You're a Fucking Shithead"
3.) go away
5.) Someone who is a fucking slut.
6.) Someone who is a slut in the act of fucking.
2.) YAFS!!! STOP EATING MY STROMBOLLI
3.) Yafs, Charizard is so the best.
4.) Yafs, thats why I fucked you.
5.) Yafs, someone needs to ram a flaming iron spike of acid in your anal cavity you goddamn slut.
6.) You got domed by whats her face, that yafs.
7.) You just got picked up by some yafs... wait thats your mom.
8.) YAFS MOM!!!!!
You: YAF you friggin tool.
It is popular to use on the internet but some say it face to face. An example would be calling your friend a YAF for example....
Ralph: GMF, yaf.
*also see GMF for meaning.